Donald Trump speaks at the White House on Wednesday in Washington DC.
Photograph: Chip Somodevilla/Getty Images

A clear majority of Americans believe Donald Trump has tried to interfere with the investigation into Russia’s alleged election meddling and possible Trump campaign collusion, a new poll shows. Just one in five support his decision to oust James Comey from the FBI.

Following Comey’s appearance before Congress last week, an Associated Press-NORC Center for Public Affairs Research poll shows 68% of Americans are at least moderately concerned about the possibility that Trump or his campaign associates had inappropriate ties to Russia. Almost half of Americans say they’re very concerned. Only three in 10 say they’re not that concerned.

Americans largely view the issue along partisan lines. Sixty-two percent of Republicans say they’re not very concerned or not at all concerned about any Russia ties. Though just over half of Americans say they disapprove of Trump’s firing of Comey, the number grows to 79% among Democrats. Overall, only 22% of Americans support Comey’s dismissal.

For Sandra Younger, a 50-year-old from San Diego, Comey’s exit reinforced her suspicion “something fishy” was going on with the president and Russia. She said it was inappropriate to fire Comey given that he was overseeing the Russia investigation.

“If I had nothing to hide and someone wanted to investigate, I would say, ‘Go ahead, do your thing, I don’t care, because you won’t find anything,’” said Younger, a Democrat who imports jewelry supplies. She added of Trump: “He seems to be buddy-buddy with these epic creeps.”

But William Shepherd, a maintenance worker from Anderson, Indiana, felt it was the president’s prerogative to choose his FBI director. He said he was untroubled by claims Trump tried to persuade Comey to back off the investigation, saying those revelations only emerged after Comey was fired and wanted to defend himself.

“These headlines don’t really concern me, although they are attention-grabbers,” said Shepherd, a 40-year-old Republican.

Of the six in 10 Americans who think Trump tried to obstruct or impede the investigation, most are Democrats and independents. Only a quarter of Republicans feel Trump meddled in the probe.

The poll began the day before Comey testified publicly before the Senate intelligence committee and continued through Sunday. Three percent of interviews were conducted before the hearing.

For many Democrats, there’s some irony in coming to Comey’s defense and embracing his concerns about Trump. Last year, Democrats aggressively attacked Comey for his handling of the Hillary Clinton email investigation, with many calling for his firing.

Now that Trump is president and Comey has emerged as a top Trump antagonist, some former Comey critics see his willingness to go after the leaders of both political parties as proof of his independence.

“I’ve not ever been a particular fan of Mr Comey’s,” said James Shaw, 53, of Olney, Illinois, pointing to the Clinton saga as a key reason. “But he’s an honest broker. I don’t think he’s politically motivated. I don’t think he’s partisan.”

Trump’s reference to the Russia probe as a reason for firing Comey bothers Linda Richardson, 62 – but not enough to second-guess his decision. Richardson, who said she’s a registered Democrat but has voted Republican for years, said Trump might have had other reasons, too.

“I guess you feel like you just need to trust your president,” said Richardson, a retiree from Meade County, Kentucky. “He just knows more about it than I do.”

Americans are mixed on whether the justice department investigation, now led by Robert Mueller, can be fair and impartial. Twenty-six percent are very or extremely confident it can be. Thirty-six percent are moderately confident and an equal share of Americans aren’t very confident or are not at all so.

Mueller, the former FBI director, was put in charge of the investigation after Trump fired Comey and public pressure mounted for a special counsel to take over. Comey later testified that he’d authorized a friend to disclose to the media his notes on conversations with Trump about the investigation, in hopes that it would lead the justice department to name a special counsel.

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The poll shows the public relatively unsympathetic to those leaking information about the investigation. Fifty-four percent say they’re doing more harm than good by potentially damaging national security. Forty-two percent think they’re doing more good by giving the public necessary information.

In general, 29% of Americans say they have a great deal of confidence in the people running the FBI. Fifty-two percent have a moderate amount of confidence and 18% have hardly any confidence. Democrats are more likely than Republicans to say they have a great deal of confidence in the FBI, 38% to 24%.

• The AP-NORC poll of 1,068 adults was conducted 8-11 June using a sample drawn from NORC’s probability-based AmeriSpeak panel, which is designed to be representative of the US population. The margin of sampling error for all respondents is plus or minus 4.1 percentage points. Respondents were first selected randomly using address-based sampling methods, and later interviewed online or by phone